Cybex booster amazing, now what?

I can't decide if I should 5 pt. harness until my kid is 30 or use an awesome booster?

So today my new Cybex X-fit + booster arrived. This is the one that's sold in the US now but is top rated in Europe. It's like a carseat that went to Harvard. I am amazed, truly. I love it. When should I use it? Read on...

My 3.5 and 4.5 year-olds are in Radian XT's FF in the 5 pt. harness. Very good, and I plan to keep them there. I know they are safe in the Radians (which seem to have excellent side-impact protection and sturdy headrests), and I'm glad I didn't go with other seats for them. Though the Radians are a far cry from Cybex, even.

The Cybex is just for carpools and a spare seat. It's too well-padded, wonderful and safe for a spare, but here it sits in the basement.

Anyone ever played with the Cybex up close? Are my kids best off in the Radians until they outgrow them (maybe age 6 or 7)? Technically the kid about to be 5-year-old could be in a booster, but I know 5 pt. is safer. Is he safer even though the Cybex seems to offer much better protection? Again I'm thinking mainly side-impact stuff (that Europe is awesome with!). The Radians do have that steel frame, so I guess that's good enough, right? I'm a huge fan of harness as long as possible, but seeing this booster just leaves me with questions!

There is no evidence that harnessing is safer than boostering, for children who can use boosters properly. Proper use includes physical and developmental maturity, impulse control, and not-messing-with-belts-ness.

Very very few 4yos are ready for boosters, and most newly-5yos are not either. So while we can't conclude that harnessing as long as possible is always safest, we're pretty sure it's safest for 4yos and new 5yos.

Using ketchupqueen's recent accident as as example, I personally think that until they are a little bigger and a little older, a 5 point harness is likely safer in a rollover or t bone. I know that's really just my opinion, and we have no studies to prove that harnessing is safer once they reach a safe booster size and maturity level. But anecdotally, it makes sense to me. If they were 8-9 yrs old or big 6-7 yrs olds, I think it's a toss up.

GL!

henrietta